1. Field of the Invention
The present invention relates generally to a toner jet recording apparatus in which particle flows are modulated, and more particularly to a technique for preventing apertures of a particle-flow modulating electrode member from being plugged with the toner particles.
2. Discussion of the Prior Art
An example of a toner jet recording apparatus is disclosed in U.S. Pat. No. 3,689,935 to G. L. Pressman et. al. This recording apparatus includes a toner supply, a back electrode, and a particle-flow modulating electrode member disposed between the toner supply and the back electrode. A recording medium is passed between the modulating electrode member and the back electrode. The toner supply delivers a crowd of electrostatically charged toner particles, so that the crowd of the charged particles remains near the modulating electrode member. With controlled electric signals being applied to the back electrode and modulating electrode member, flows of the particles through multiple apertures of the modulating electrode member are selectively modulated. More specifically, the modulating electrode member consists of an insulating layer, a first electrode in the form of a conductive layer provided on one side of the insulating layer, and second electrodes in the form of an array of conductive strips provided on the other side of the insulating layer. The modulating electrode member has a multiplicity of apertures formed through the insulating layer and the first electrode layer and through the respective conductive strips of the second electrode. The back electrode is disposed in opposed relation with the modulating electrode member, so as to back the recording medium such as a paper sheet, and also functions to attract the particle flows through the apertures to the surface of the recording medium. Thus, the toner jet recording apparatus is adapted to effect recording on the recording medium, by modulating the flows of the charged toner particle such that the particle flows pass through the selected apertures according to the controlled electric signals applied to the modulating electrode member.
However, the known toner jet recording apparatus as described above suffers from plugging or filling of the apertures of the modulating electrode member with the toner particles. If the desired recording density is 240 DPI (dots per inch), the maximum size of image dots is 100 .mu.m, and the maximum inside diameter of each aperture of the modulating electrode member should be as small as 50 .mu.m. On the other hand, the toner particles tend to be deposited on the surfaces of the modulating electrode member due to the effect of the image force. Under this condition, the apertures are likely to be plugged or filled with the toner particles during use of the recording apparatus, deteriorating the image forming stability or reliability of the apparatus.